Protective Sheath for an Endoscope

ABSTRACT

A protective sheath for an endoscope includes an elongated shaft with a longitudinal bore extending from a proximal opening at the shaft proximal end to a distal opening at the shaft distal end. The longitudinal bore is sized for receiving an endoscope tube inserted axially into the bore. The shaft distal end includes a hood having a proximal portion and a distal portion and defining a hood interior space. The hood proximal portion has a width that is greater than a maximum width of the shaft at the bore distal opening. The hood proximal portion defines an opening to the hood interior space, which opening is laterally offset from the shaft distal end and is configured to receive a portion of a surgical instrument within the hood interior space.

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 13/912,312, filed on Jun. 7, 2013, which claims the benefit of U.S. Provisional Application No. 61/656,989, filed Jun. 7, 2012, and entitled “Protective Sheath for an Endoscope,” which is incorporated herein in its entirety by this reference.

BACKGROUND

This invention relates to an apparatus for use in performing endoscopic surgical procedures. More particularly, the invention relates to an improved sheath for an endoscope for performing surgical procedures requiring fibrous tissue division, such as an endoscopic procedure for carpal tunnel release.

Because of the trauma associated with open surgical procedures, efforts have been made to develop endoscopic alternatives to all types of open surgical procedures. This invention relates to endoscopic alternatives to open procedure for surgical treatments requiring division of soft tissue, such as a tendon sheath or ligament. One example of such a procedure is the treatment of carpal tunnel syndrome, caused by the compression of the median nerve by the transverse carpal ligament. This treatment generally involves a procedure during which the carpal ligament is severed. While endoscopic versions of this procedure have been used in the past with varying degrees of success, continued development of endoscopic procedures to improve efficiencies and reduce patient trauma is always desirable.

For example, the prior endoscopic treatments of carpel tunnel syndrome described by Chow in U.S. Pat. No. 5,029,573 and by Brown in U.S. Pat. No. 5,323,765 use a slotted cannula design that is positioned under the transverse carpal ligament during the procedure. This places pressure on the nerve during the procedures and also places the nerve and tendons at risk of injury. Moreover, a number of prior endoscopic procedures for carpel tunnel release require two incisions (with one being in the palm) and/or require the introduction of one or more obturators into the carpel tunnel before insertion of the endoscope, which can cause additional trauma to the surgery site.

Accordingly, it is an object of the present invention to produce an endoscopic surgical apparatus suitable for use in various surgical procedures that involve the dissection and/or other retraction of fibrous tissue, including an endoscopic procedure for carpal ligament release as well as other endoscopic surgical procedures.

It is another object of the invention to provide an apparatus for performing such endoscopic surgical procedures with less trauma than existing endoscopic procedures.

It is another object of the present invention to provide an apparatus that facilitates the alignment of a cannula over the carpal ligament.

Although one preferred embodiment of this invention relates to carpal ligament release, it will be understood by those skilled in the art that the apparatus disclosed herein may be easily adapted to other surgical procedures.

Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations pointed out in the appended claims.

SUMMARY

To achieve the foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, there is provided a protective sheath for an endoscope that includes an elongated shaft that is disposed along a shaft axis and includes a distal end and a proximal end. The shaft has a longitudinal bore extending from a bore proximal opening at the shaft proximal end to a bore distal opening at the shaft distal end. The longitudinal bore is sized for receiving an endoscope tube inserted axially into the bore from the shaft proximal end. The shaft distal end includes a hood having a proximal portion and a distal portion and defining a hood interior space. The hood proximal portion has a width that is greater than a maximum width of the shaft at the bore distal opening. The hood proximal portion defines an opening to the hood interior space, which opening is laterally offset from the shaft distal end and is configured to receive a portion of a surgical instrument within the hood interior space. In this sheath configuration, a surgeon can slide a surgical instrument, such as tenotomy scissors, along the sheath and through the hood proximal opening into the hood interior space to cut tissue with improved visualization of anatomy.

In some embodiments, the hood cover includes a sloped surface that extends longitudinally toward and terminates at the forward-projecting edge. The hood distal portion can be a generally flat surface terminating in a forward-projecting cutting edge disposed generally perpendicular to the shaft axis and adapted for cutting muscle, fat or other soft tissue.

In some embodiments, one or more surfaces of the hood are adapted for retracting soft tissue during a surgical procedure. For example, the hood can include a generally planar flange that has a rib projecting outwardly beyond an outermost portion of a hood sidewall. As another example, the hood can include a sidewall that extends laterally outward from the hood cover.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the presently preferred embodiments and methods of the invention and, together with the general description given above and the detailed description of the preferred embodiments and methods given below, serve to explain the principles of the invention.

FIG. 1 is a perspective view of one embodiment of a sheath that can be used for endoscopic surgical procedures and that includes some features of the present invention.

FIG. 2 is a side elevation view of the sheath of FIG. 1.

FIG. 3 is a plan view of the sheath of FIG. 1 showing the hood interior space.

FIG. 4 is another plan view of the sheath shown in FIG. 1.

FIG. 5 is an elevation view of the proximal end of the sheath shown in FIG. 1.

FIG. 6 is a cross-sectional view taken along the line A-A shown in FIG. 3.

FIG. 7 is a cross-sectional view taken along the line B-B shown in FIG. 2.

FIG. 8 is a cross-sectional view taken along the line C-C shown in FIG. 2.

FIG. 9 is an enlarged view of a portion of the sheath of FIG. 1, which portion is referenced as detail D in FIG. 4.

FIG. 10 is an enlarged view of a portion of the sheath of FIG. 1, which portion is referenced as detail E in FIG. 3.

FIG. 11 is an enlarged view of a portion of the sheath of FIG. 1, which portion is referenced as detail F in FIG. 2.

FIG. 12 is an enlarged view of a portion of the sheath of FIG. 1, which portion is referenced as detail Gin FIG. 3.

FIG. 13 is a cross-sectional view taken along the line H-H shown in FIG. 12.

FIG. 14 is a side perspective view of an alternative embodiment of a sheath according to the present invention.

FIG. 15 is another side perspective view of the sheath of FIG. 14.

FIG. 16 is a side elevation view of the sheath shown in FIG. 14.

FIG. 17 is a plan view of the sheath shown in FIG. 14.

FIG. 18 is an elevation view of the proximal end of the sheath shown in FIG. 14.

FIG. 19 is a cross-sectional view taken along the line A-A shown in FIG. 17.

FIG. 20 is a perspective view from the distal end of another embodiment of a sheath according to the present invention, which embodiment includes a hood with an opening configured to receive a portion of a surgical instrument within the hood interior space.

FIG. 21 is a perspective view from the proximal end of the sheath of claim 20 showing the distal end of the sheath.

FIG. 22 is a perspective view of the sheath of claim 20 showing the hood interior space.

FIG. 23 is a plan view of the sheath of claim 20 showing the hood interior space.

FIG. 24 is perspective view from the proximal end of the sheath of claim 20 showing both the proximal and distal ends of the sheath.

FIG. 25 is a plan view of the distal end of the sheath of claim 20 showing dimensions of one embodiment of the hood.

DESCRIPTION

Reference will now be made in more detail to presently preferred embodiments of the invention, as illustrated in the accompanying drawings. While the invention is described more fully with reference to these examples and drawings, the invention in its broader aspects is not limited to the specific details, representative devices, and illustrative examples shown and described. Rather, the description which follows is to be understood as a broad, teaching disclosure directed to persons of ordinary skill in the appropriate arts, and not as limiting upon the invention.

As used herein, the term “endoscope” is intended to be generic and refers to any type of optical system used to view the interior of a patient. It also will be appreciated that terms such as “upper,” “inner,” “outer,” “vertical,” “horizontal,” “bottom,” “below,” “top,” “side,” “inwardly,” “outwardly,” “downwardly” and “lower” and other positionally descriptive terms used in this specification are used merely for ease of description and refer to the orientation of the referenced components as shown in the figures. It should be understood that any orientation of the components described herein is within the scope of the present invention. The term “generally” as used in this specification is defined as “being in general but not necessarily exactly or wholly that which is specified.” For example, “generally perpendicular” is used herein to indicate components that are in general, but not necessarily exactly or wholly, perpendicular.

In the drawings, the reference numeral 10 designates a protective sheath for an endoscope. The sheath 10 comprises an elongated cannula or tubular shaft 12 with a longitudinal bore 17 extending along the axis of the shaft 12 from an opening at a sheath proximal portion 16 (also sometimes referred to in this specification as the sheath proximal end) to an opening at a sheath distal portion 14 (also sometimes referred to in this specification as the sheath proximal end). The shaft 12 includes a shaft distal section 18 (also sometimes referred to in this specification as the shaft distal end) at the sheath distal portion 14, a larger-diameter shaft proximal section 20 (also sometimes referred to in this specification as the shaft proximal end) at the sheath proximal portion 16, and a shaft tapered section 22 intermediate the shaft distal section 18 and the shaft proximal section 20.

The width of the bore 17 should be sufficient to enable the chosen endoscope to slide freely into the bore 17. If it is too wide, the surgeon would have to be too concerned about aiming the scope. In some embodiments, the portion of the bore 17 within the shaft distal section 18 is from about 0.11 to 0.12 inches (or from about 2.7 to 3.0 millimeters). In this configuration, the bore 17 can accept a standard 2.7 millimeter endoscope tube. To permit easy insertion of an endoscope tube into the sheath 10, the bore 17 is enlarged inside the shaft proximal section 20 and is tapered in the shaft tapered section 22.

The sheath distal portion 14 includes a generally shovel-shaped hood 30, which is used to assist with the dissection and retraction of soft tissue during use. As can be seen in FIGS. 2-4, 6, 9-10, and 22-24, in some embodiments, the hood 30 includes a cover 32 that curves gradually downward and terminates at its distal end in a relatively flat edge to form a cutting tip 34. Two sidewalls 36 a, 36 b extend downwardly from the hood cover 32 and terminate in sidewall rims 38 a, 38 b along the lower portion of the hood 30. In some embodiments (see FIGS. 2-4, 6, and 9-10), these rims 38 a, 38 b are in the form of flanges that include outwardly projecting ribs that extend beyond an outermost portion of the corresponding hood sidewall 36 a, 36 b. In this configuration, the cutting tip 34 can be used to dissect soft tissue during a procedure, and the outer surfaces of the sidewalls 36, the hood cover 32 and the sidewall flanges 38 can be used to assist with the retraction of soft tissue (e.g., muscle and fat) during a procedure. In a presently preferred embodiment, the sidewalls are solid and are light-reflective to reflect light transmitted from the endoscope tube toward the desired work site. However in an alternative embodiment, as shown in FIGS. 14-19, the hood side walls 36 can include orifices.

The sheath 10 includes a collar 24 to which is mounted an attachment mechanism 25 that can be securely attached to the face of an endoscopic camera to prevent rotation or longitudinal movement of the camera and the endoscopic tube with respect to the sheath 10. As shown in FIGS. 2-5, 7-8 and 11, in some embodiments, the collar 24 is in the shape of a generally rectangular plate and the attachment mechanism 25 includes a first clip 26 (comprising a pair of first clip prongs 26 a, 26 b) and a second clip 28 (comprising a pair of second clip prongs 28 a, 28 b). In this configuration, the collar 24 and attachment mechanism 25 are configured to easily and securely attach to the face of an endoscopic camera such as those marketed by Stryker Corporation of Kalamazoo, Mich.

While any known material can be used to build this device, it is preferable to use medical grade stainless steel. Similarly, it is preferred to build the entire protective sheath out of a single piece of material, such as by machining the device from a single stainless steel work-piece. However, the device can be built with any known metalworking technique. Exemplary dimensions of one embodiment of the sheath 10 are shown (in inches) in FIGS. 3, 5-9, 11 and 13, and exemplary dimensions of another alternative embodiment are shown (in millimeters) in FIGS. 17-19.

To use the device, a physician slides the endoscope tube (not shown) into the bore 17 through the opening in the collar 24 and through the shaft proximal section 20, the shaft tapered section 22 and the shaft distal section 18 so that the endoscope rests within the hood 30 at the distal portion 14 of the sheath. The endoscope can then be used to illuminate and view the work area as is known in the art.

For performing endoscopic tendon surgery, the sheath 10 can be placed over an endoscope and inserted into the area of dissection. The sheath 10 then facilitates dissection of the soft tissues over the tendon with visualization and retraction of the nerves to allow release of the tight tunnel for the tendon. For nerve surgery, the sheath 10 also can be placed over an endoscope and inserted into the area of dissection. The sheath 10 facilitates retraction of soft tissues and visualization of the nerves. Because of the free movement allowed with the sheath 10, small scissors can then be placed to perform release of scar tissue or placement of anti-adhesive barriers to prevent further scar tissue.

Referring specifically to FIGS. 20-25, in some embodiments, the sheath 10 includes a hood 30 that has a proximal opening 40 sized for receiving a portion of a surgical instrument inserted into a hood interior space 42. In this configuration, a surgeon can slide the distal end of the surgical instrument along the shaft 12 and insert the distal end of the surgical instrument through the hood proximal opening 40 and into the protected hood interior space 42. This provides an easier path for the surgeon to use the instrument (such as tenotomy scissors used to dissect and cut tissue) with improved visualization of the patient's anatomy.

In the embodiment of FIGS. 20-25, the hood cover 32 and opposing sidewalls 36 a, 36 b define the hood interior space 42. The hood 30 has a distal portion 44 that terminates in a forward-projecting edge at the cutting tip 34, which is adapted for cutting muscle, fat or other soft tissue. The hood 30 also has a proximal portion 46 with a width that is greater than a maximum width of the shaft 12 at the bore distal opening. The hood proximal portion 46 defines the hood proximal opening 40, which is in communication with the hood interior space 42. The hood proximal opening 40 is laterally offset from the shaft distal section 18 and is configured to receive a portion of a surgical instrument within the hood interior space 42. For example, as can be seen in FIGS. 20 and 21, the hood proximal opening 40 can be a slotted opening extending from the hood cover 32 to the rim 38 a of sidewall 36 a. FIG. 25 shows the dimensions of one advantageous embodiment of the hood 30. Although not shown in FIGS. 20-25, it will be understood upon reading this disclosure that each of the hood sidewall rims 38 a, 38 b can include a flange with an outwardly projecting rib like that previously described.

The sheath 10 according to the present invention can be used in a number of different endoscopic procedures, including the following:

Endoscopic carpal tunnel release

Endoscopic cubital tunnel release

Endoscopic pronator release

Endoscopic De Quervains release

Endoscopic trigger finger release

Endoscopic trigger thumb release

Endoscopic tennis elbow surgery

Endoscopic tenolysis for adhesions

Endoscopic tendon transfer

Endoscopic Dupuytren's fasciectomy

For illustrative purposes, certain of these procedures will now be described in more detail.

Procedure for Endoscopic Dequervain's Release

The first dorsal compartment is palpated over the radial styloid and a 5-10 mm transverse incision is marked between the radial styloid and base of first metacarpal. The incision is carried down through the skin and subcutaneous tissue until the tendons of the first dorsal compartment (APL, EPB) are visualized. Next, the endoscopic sheath 10 is placed over an endoscopic camera and locked into position. The sheath and camera are then placed into the incision from a distal to proximal direction obtaining visualization of the first dorsal compartment tendons. The cutting tip 34 of the sheath 10 is then used to dissect over the first dorsal compartment from distal to proximal. If the superficial branch of the radial nerve is identified over the compartment, it can be retracted away from the field using the hood 30 of the sheath 10. The thickened compartment is then divided along the middle portion of the compartment from distal to proximal direction using tenotomy scissors. This will leave approximately equal flaps on either side to prevent subluxation of the tendons. Next, the thumb is placed through a full passive flexion and extension motion to ensure complete release of the compartment. The sheath 10 is then used to visualize the compartment release and identify any separate compartments. Any separate compartments can then be released under direct visualization of the endoscopic sheath 10 and tenotomy scissors dividing the additional compartments in a distal to proximal direction. The sheath 10 and camera are then removed slowly while ensuring complete release of all compartments within the first dorsal compartment region. The skin edges are then closed with a dermal suture and dressed with steri-strip skin closures and soft dressing. Motion is started the day of surgery with 5 pound restrictions and then full activity allowed by one week.

Procedure for Endoscopic Trigger Thumb Release

A transverse incision is marked on the volar aspect of the thumb 1.5 cm distal to the proximal-proximal thumb flexion crease. This incision should be on the volar aspect of the thumb in line with the middle portion of the distal thumb flexion crease, to correspond with the flexor pollicis longus (“FPL”) tendon. The incision is carried down through skin and subcutaneous tissues until the FPL tendon is visualized.

The sheath 10 is then placed over an endoscopic camera and locked into position. The sheath 10 and camera are then introduced into the incision in a distal to proximal direction. The cutting tip 34 is used to dissect over the surface of the FPL and a 1 pulley (i.e., the tight tunnel that the tendon travels through before it attaches to the bone, release of which allows easier motion and reduces the pain from trigger finger). If the Neurovascular bundle is present, it can be dissected out of the field using the hood 30 of the sheath to protect the pulley during division. The pulley is then divided using tenotomy scissors under direct visualization. The thumb is placed through a passive flexion and extension range of motion ensuring complete release of the pulley. The instruments are then withdrawn slowly, again ensuring complete release of the pulley. The skin edges are then closed using dermal sutures and steri-strip skin closures and soft dressing applied. The patient begins immediate motion with five pound restrictions and unrestricted activity at one week.

Procedure for Endoscopic Carpal Tunnel Release and Neurolysis

A 5-10 mm transverse incision is placed 1 cm proximal to the distal volar wrist crease and ulnar to the palmaris longus tendon. This incision is carried down through the skin and subcutaneous tissue until the volar fascia is identified. The fascia is then divided using tenotomy scissors.

The sheath 10 is then placed over an endoscopic camera and locked into place. The sheath 10 and camera are then introduced into the incision from a proximal to distal direction over the volar fascia. The fascia is then divided from proximal to distal using tenotomy scissors under direct visualization. The dissection is continued distally using the cutting tip 34 of the sheath 10 to assist with soft tissue dissection over the transverse carpal ligament (extension of fascia distally). This ligament is divided using tenotomy scissors under direct visualization of the sheath 10 and camera from proximal to distal until the distal edge is completely released. During the division of the ligament the nerve will be visualized below the divided ligament ensuring complete release of pressure on the nerve.

After complete release, the sheath and camera are withdrawn slowly to obtain visualization of the median nerve and ensure no other scar tissue or other pathology exists which may cause continued symptoms of nerve compression. Any other areas of median nerve tethering or scar tissue can be released under direct visualization using the sheath and tenotomy scissors to divide the tissue. This procedure is the first endoscopic technique able to perform a neurolysis. For recurrent nerve compression and scar tissue cases, a small piece of non-adhesive barrier can he placed through the incision using a small clamp under direct visualization for placement directly on top of the median nerve to prevent further adhesions. After completion of the procedures, the sheath 10 is then withdrawn slowly ensuring complete release of the median nerve. The skin edges are closed using a dermal suture and steri-strip skin closures. Marcaine and corticosteroids and injected for post-operative pain control and the hand dressed with soft dressings. Motion is started immediately with five pound restrictions for the first week and unrestricted activity by one week.

Procedure for Endoscopic Fasciotomy for Tennis Elbow

A 1 cm longitudinal incision is placed 2 cm distal to the lateral epicondyle. This incision is carried down through the skin and subcutaneous tissues. The sheath 10 is then placed over an endoscopic camera and locked in place. The sheath 10 is then placed into the incision and the cutting tip 34 is used to dissect the soft tissue off the extensor tendon fascia. Tenotomy scissors are then used to release the fascia of the extensor carpi radialis longus, extensor carpi radialis brevus and extensor digitorum. The dissection is also carried down to the supinator, and the fascia over this muscle is also released under direct visualization of the sheath. The sheath 10 is then withdrawn slowly to ensure complete release of the fascia. The skin edges are then closed with a dermal suture and steri-strip skin closures. Soft dressing is then applied and immediate motion allowed with five pound restrictions for the first week and unrestricted activity after one week.

From the foregoing it should be apparent that endoscope sheath of the present invention provides a number of advantages over previous endoscopic tools and procedures. It provides an endoscopic surgical apparatus suitable for use in various surgical procedures that involve the dissection and/or other retraction of fibrous tissue, including an endoscopic procedure for carpal ligament release as well as other endoscopic surgical procedures. The apparatus can be used to perform such endoscopic surgical procedures with less trauma than previous endoscopic procedures. For example, during a carpel ligament release procedure, it can be placed over the carpal ligament and can provide a clear visualization of the nerve during the procedure, minimizing trauma to the nerve and also significantly reducing any chance of injury.

Having read this disclosure, it will also be understood by those having skill in the art that modifications may be made to the invention. Therefore, the invention in its broader aspects is not limited to the specific details, representative devices, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concept. 

What is claimed is:
 1. A protective sheath for an endoscope, the sheath comprising: an elongated shaft disposed along a shaft axis and including a distal end and a proximal end and having a longitudinal bore extending from a bore proximal opening at the shaft proximal end to a bore distal opening at the shaft distal end; wherein the longitudinal bore is sized for receiving an endoscope tube inserted axially therein; and a hood disposed at the shaft distal end, wherein the hood comprises a hood proximal portion and a hood distal portion and defines a hood interior space; and wherein the hood proximal portion has an opening to the hood interior space, which opening is laterally offset from the shaft distal end and is configured to receive a portion of a surgical instrument within the hood interior space.
 2. The sheath of claim 1 wherein the hood includes a sidewall disposed generally perpendicular to a hood cover.
 3. The sheath of claim 2 wherein the hood cover includes a sloped surface that extends longitudinally toward and terminates at a forward-projecting edge.
 4. The sheath of claim 3 wherein the forward-projecting edge is disposed generally perpendicular to the shaft axis and extends for a distance that is greater than a maximum width of the bore distal opening at the shaft distal end.
 5. The sheath of claim 1 wherein one or more surfaces of the hood are adapted for retracting soft tissue during a surgical procedure.
 6. The sheath of claim 3 wherein the forward-projecting edge is adapted for cutting muscle, fat or other soft tissue.
 7. The sheath of claim 1 further comprising a clip disposed at the shaft proximal end, wherein the clip is configured for attachment to an endoscopic camera.
 8. The sheath of claim 2 wherein the opening to the hood interior space comprises a slot that extends from the hood cover to a sidewall rim opposite the hood cover.
 9. A protective sheath for an endoscope, the sheath comprising: an elongated shaft disposed along a shaft axis and including a distal end and a proximal end and having a longitudinal bore extending from a bore proximal opening at the shaft proximal end to a bore distal opening at the shaft distal end; wherein the longitudinal bore is sized for receiving an endoscope tube inserted axially into the bore from the shaft proximal end; and a hood disposed at the shaft distal end, wherein the hood comprises: a hood cover and a pair of opposing sidewalls that define a hood interior space; a hood distal portion comprising a generally flat surface terminating in a forward-projecting cutting edge adapted for cutting muscle, fat or other soft tissue; and a hood proximal portion having a width that is greater than a maximum width of the shaft at the bore distal opening; wherein the hood proximal portion defines an opening to the hood interior space, and the hood proximal opening is laterally offset from the shaft distal end and is configured to receive a portion of a surgical instrument within the hood interior space.
 10. The sheath of claim 9 wherein the hood further comprises a generally planar flange including a rib that projects outwardly beyond an outermost portion of one of the sidewalls.
 11. The sheath of claim 10 wherein the forward-projecting cutting edge is disposed generally parallel to the planar flange and generally perpendicular to the shaft axis, and the forward-projecting cutting edge has a extends for a distance greater than a maximum width of the bore distal opening at the shaft distal end.
 12. The sheath of claim 9 further comprising a clip disposed at the shaft proximal end, wherein the clip is configured for attachment to an endoscopic camera.
 13. The sheath of claim 9 wherein at least one of the sidewalls comprises a light-reflective surface.
 14. The sheath of claim 9 wherein the hood includes one or more surfaces adapted for retracting soft tissue during a surgical procedure.
 15. The sheath of claim 9 wherein the opening to the hood interior space comprises a slot that extends from the hood cover to a rim of one of the sidewalls wherein the rim is opposite the hood cover.
 16. A protective sheath for an endoscope comprising: an elongated shaft disposed along a shaft axis and including a distal end and a proximal end and having a bore extending longitudinally from a bore proximal opening at the shaft proximal end to a bore distal opening at the shaft distal end; wherein the longitudinal bore is sized for receiving an endoscope tube inserted axially therein; wherein the shaft distal end includes a shovel-shaped hood having an interior space and comprising: a hood cover and a sidewall extending from the cover to a rim that includes a generally planar flange disposed opposite the hood cover, wherein the flange comprises a rib disposed generally parallel to the shaft axis and projecting outwardly beyond an outermost portion of the sidewall; a hood distal portion comprising a generally flat surface disposed generally parallel to the shaft axis and having a forward-projecting distal edge disposed generally perpendicular to the shaft axis; and a hood proximal portion having a width that is greater than a maximum width of the shaft at the bore distal opening; wherein the hood proximal portion defines an opening to the hood interior space, which opening is laterally offset from the shaft distal end and is configured to receive a portion of a surgical instrument within the hood interior space.
 17. The sheath of claim 16 wherein the hood proximal opening comprises a slot.
 18. The sheath of claim 17 wherein the slot extends from the hood cover to the sidewall rim.
 19. The sheath of claim 16 wherein the hood forward-projecting distal edge extends for a distance that is greater than the maximum width of the bore distal opening at the shaft distal end. 